The storage-life of oxidatively-degradable foodstuffs such as fish, meat, poultry, bakery goods, fruits, grains, and vegetables is limited in the presence of a normal atmospheric environment. The presence of oxygen at levels found in a normal atmospheric environment leads to changes in odor, flavor, color, and texture resulting in an overall deterioration in quality of the foods either by chemical effect or by growth of aerobic spoilage microorganisms.
Modified atmosphere packaging (MAP) has been used to improve storage-life and safety of stored foods by inhibition of spoilage organisms and pathogens. MAP is the replacement of the normal atmospheric environment in a food storage pack with a single gas or a mixture of gases. The gases used in MAP are most often combinations of oxygen (O2), nitrogen (N2), and carbon dioxide (CO2). In most cases, the bacteriostatic effect is obtained by a combination of decreased O2 and increased CO2 concentrations. Farber, J. M. 1991. Microbiological aspects of modified-atmosphere packaging technology: a review. J. Food Protect. 54:58-70.
In traditional MAP systems, the MAP gas composition is not manipulated after the initial replacement of the normal atmospheric environment. Thus, the composition of the gases present in the food pack is likely to change over time. In certain cases, the foodstuff will absorb CO2 reducing the amount of carbon dioxide in the gas portion of the packaging with a concomitant increase in the relative amounts of other gases such as oxygen. Still further changes in the gas portion of the packaging can be due to diffusion of gases into and out of the product, and the effects of microbiological metabolism. Carbon dioxide absorption can lead to a negative pressure in the tote creating a “vacuumizing” situation which could potentially damaging the foodstuff by, e.g., reducing the carbon dioxide concentration below levels effective for inhibiting microbial spoilage of the foodstuff with corresponding increases in residual oxygen concentrations. Vacuumization caused by CO2 absorption can also cause leakage, especially in rigid totes, resulting in failures.
The use of MAP systems and related technologies has been in use for shipping and storage of foodstuff. However, these systems imposed significant limitations on the delivery of food stuffs that are sensitive to oxidative degradation, such as fish. First and most important, the cooling and oxygen removal processes of these systems were integrated into a single sealed container (typically a refrigerated freight container—a reefer unit) such that upon opening the entire shipment was exposed to the ambient atmospheric conditions. This limited the ability to split the foodstuff into different delivery sites and typically required that the vendee acquire the entire product upon opening. Second, the integration of the oxygen removal process into the container dictated that inadvertent or premature breakage of the seal in the sealed container put the entire product at risk. Third, the integration of the oxygen removal processes into the freight container did not permit separate atmospheric conditions within the container during storing and/or transporting thereby limiting the flexibility of the process. Fourth, sealing of a freight container posed difficulties especially when the atmospheric pressure within the container became less than that outside of the container. The most common MAP applications employ a bag-in-box architecture whereby the perishable is contained inside a bag/package that is contained inside a box/carton. The bag/package is gas flushed one or more times to create the desired modified atmosphere before the bag/package is heat sealed and the box closed. This system may or may not employ excess headspace to allow for overfilling of gases such as CO2 that are absorbed by many perishables. The typical constraint on how much excess headspace can be employed is the requirement that these MAP packages be unitized (stacked) for transport and handling. This architectural constraint dictates an external carton or box that can be closed around the bag/package and stacked and easily handled throughout the supply chain. Consequently, the “excess” headspace designed into these architectures is inadequate to prevent a decrease in CO2 partial pressures over time with a corresponding increase in oxygen.
In addition to traditional MAP systems as discussed above, systems for transporting perishable foodstuffs using an external fuel cell to remove oxygen have been developed, such as disclosed by U.S. Pat. No. 6,179,986. This patent does not describe the use of a fuel cell but instead it discloses the use of a proton exchange membrane (PEM) stack based solid polymer electrolyte (EOC) electrochemical oxygen control system which is operated differently than a fuel cell and requires the application of DC power. The PEM is operated external to the sealed container to the extent that it required venting of at least one of the products of the fuel cell reaction to the outside of the sealed container. Additionally, the system described in the '986 patent required the use of a dedicated power supply to provide power to the fuel cell.
The systems described above have many disadvantages that make them undesirable for long-term transporting or storing of foodstuff that is oxidatively degradable. Thus, the need exists for an improved system that would increase the storage-life of oxidatively-degradable materials during transport and storage that avoids the disadvantages of conventional shipping and storage techniques. Additionally, it would be advantageous to have the ability to transport and then remove modular packages of the transported foodstuff at various destinations without compromising the preserving environment of the packages.